Lunch begins at noon
Abstract: Recent years have seen increased interest in antiferromagnets, and other states of matter with antiferromagnetic exchange interactions, both for their fascinating and rich fundamental physics and for their promise in applications such as spintronic memory elements. These materials promise rapid magnetization dynamics due to strong exchange interactions, but also present significant challenges for measurements and manipulation due to a vanishing net magnetic moment. The longitudinal spin Seebeck effect (LSSE), where heat is used to excite spin currents in magnetic insulator/metal systems, and its related electrical effect, spin Hall magnetoresistance (SHMR), have proven especially powerful to study a range of antiferromagnetic materials, which can be difficult to probe using more traditional magnetic characterization techniques. In this talk I will discuss our recent work on two antiferromagnetic systems, which highlight the challenges of quantifying the transition to well defined antiferromagnetism and how this state affects spin and charge flow through the material. I will present our recent results on polycrystalline chromium films, where we have used two forms of the LSSE to show that antiferromagnetism may play a role in the spin-to-charge conversion, which was not apparent from earlier work on this material [1,2]. Related electrical measurements, which probe spin Hall magnetoresistance, indicate a Hall-like signal with surprising symmetry that we have tied to oxidation of sputtered Cr, suggesting that this introduces some amount of a much more complicated magnetic character [3]. I will then discuss ongoing work on electrical probes of antiferromagnetic spin effects in field-controllable coupled ferrite/manganite, AFM/FM, perovskite oxide systems. Here, the field dependence of the electrical Hall signals correlate with signatures of Neel order in SQUID magnetometry, indicating an electrical probe of the Neel state despite reasonable expectation that the ferromagnetic and metallic manganite component dominates the charge flow in the system. The use of platinum contacts in these systems further modifies the electrical signals, suggesting a possible contribution from spin-charge conversion, but with signals that we cannot clearly disentangle due to the complexity of charge and spin flow in these, and similar systems. This work was supported by the U.S. National Science Foundation (DMR-2004646, ECCS-2116991).
1) "Negative spin Hall angle and large spin-charge conversion in thermally-evaporated chromium thin films," S. M. Bleser, R. M. Greening, M. J. Roos, L. Hernandez, X. Fan, and B. L. Zink, Journal of Applied Physics v. 131 113904 (2022).
2) "Examining the role of antiferromagnetism in spin-charge conversion in chromium thin films via temperature-dependent measurements of the local spin Seebeck effect," S. M. Bleser, M. R. Natale, R. M. Greening, X. Fan, and B. L. Zink, Physical Review Materials, v. 8 124411 (2024).
3) "Anomalous Hall-like Transverse Magnetoresistance in Sputtered Chromium Thin Films," M. R. Natale, S. M. Bleser, R. M. Greening, X. Fan, and B. L. Zink (in preparation).